This application is based on an application No. H11-290665 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an information recording medium including a plurality of sectors that are each made up of a sector header area and a data storage area, and a method and apparatus for recording and reproducing data using the information recording medium. In particular, the invention relates to an information recording medium, information recording/reproducing apparatus, and information recording/reproducing method for recording and reproducing data that is scrambled using a scramble key generated based on a sector number and a medium identifier of the information recording medium.
2. Prior Art
To protect data recorded on an information recording medium against unauthorized reproduction, techniques have been developed whereby data is scrambled or encrypted before being recorded onto an information recording medium. An unauthorized party cannot descramble or decrypt such scrambled or encrypted data properly and thus cannot reproduce the data in intelligible form.
One of the techniques for encrypting data to be recorded is disclosed in Japanese Laid-Open Patent Application No. H07-249264. According to this encryption system, after data is encrypted with an encryption key, the encrypted data and the encryption key are recorded in different sectors of a CD-ROM. Upon receiving a request to read the encryption key from the user via a personal computer, a reproducing apparatus reads the encryption key from the CD-ROM, decrypts the encrypted data using the read encryption key, and reproduces the decrypted data. The advantage of this system is that it facilitates the changing of the encryption key.
Also, one of the techniques for scrambling data to be recorded is presented by the standard developed for the physical format of DVDs.
In the aforementioned encryption system, however, the encryption key is recorded on the CD-ROM together with the encrypted data, so that an unauthorized party can easily read the encryption key and the encrypted data from the CD-ROM through the use of a device capable of reading CD-ROMs such as a general personal computer, and decrypt the encrypted data with the encryption key. Thus, the secrecy of the encryption key is not fully ensured in this system. Besides, one of the sectors of the CD-ROM is intended to store only the encryption key and cannot be used for storing data. This decreases the recording efficiency of the information recording medium.
Also, the scrambling defined by the DVD physical format standard is aimed at suppressing crosstalk between adjacent tracks, rather than protecting copyright. Which is to say, data scrambled and recorded under the DVD physical format standard can be reproduced by any reproducing apparatus that complies with this standard. Thus, this method also fails to prevent unauthorized data reproduction.
The present invention aims to provide an information recording/reproducing apparatus and method which encrypt or scramble data so that the data cannot be recovered by unauthorized means, and an information recording medium used by such apparatus and method.
The above object can be fulfilled by an information recording medium including: a first sector which has a unique sector number and stores a medium identifier unique to the information recording medium; and a plurality of second sectors each of which has a unique sector number and stores user data, wherein the user data stored in each of the plurality of second sectors has been scrambled using a data scramble key generated based on the medium identifier and the sector number of the second sector.
With this construction, user data is scrambled with a data scramble key that differs not only for each information recording medium but also for each sector. This makes it difficult for unauthorized users to reproduce data.
Here, the data scramble key may be a sequence of random numbers generated from an initial value determined based on the medium identifier and the sector number of the second sector, wherein the user data has been scrambled by performing a predetermined operation on the user data and the sequence of random numbers on a byte-by-byte basis.
With this construction, each byte of the user data to be recorded is scrambled with a different random number out of the random numbers that constitute the data scramble key, so that security against unauthorized data reproduction is further strengthened.
Here, the medium identifier stored in the first sector may have been scrambled using a medium identifier scramble key generated based on predetermined data and the sector number of the first sector.
With this construction, the medium identifier that is used for generating the data scramble key is scrambled and stored on the information recording medium. This prevents unauthorized users from acquiring the medium identifier, so that security against unauthorized data reproduction is further strengthened.
Here, the first sector may also store user data.
With this construction, it is possible to make effective use of the data storage area of the sector that stores the medium identifier.
Here, the predetermined data may be stored in a lead-in area of the information recording medium.
With this construction, only authorized users who have access to the predetermined data can acquire the medium identifier and descramble the scrambled user data using the medium identifier, so that security against unauthorized data reproduction is further strengthened.
The above object can also be fulfilled by an information recording apparatus for scrambling user data and recording the scrambled user data onto an information recording medium, the information recording medium including a first sector which stores a medium identifier unique to the information recording medium and a plurality of second sectors each of which has a unique sector number and is used for storing user data, the information recording apparatus including: an initial value determining unit for determining an initial value based on the medium identifier and a sector number of a second sector into which the user data is to be recorded; a random number generating unit for generating a sequence of random numbers from the initial value; a scrambling unit for scrambling the user data using the sequence of random numbers; and a recording unit for recording the scrambled user data into the second sector.
With this construction, user data is scrambled with a scramble key that differs not only for each information recording medium but also for each sector. This makes it difficult for unauthorized users to reproduce data.
Here, the user data may be accompanied by type information showing a data type of the user data, wherein the initial value determining unit includes: a plurality of different initial value tables corresponding to different data types; and a table selecting unit for selecting one of the plurality of initial value tables in accordance with the type information accompanying the user data, and wherein the searching unit searches the selected initial value table for the candidate initial value associated with the generated reference data.
With this construction, the initial value can be varied depending on the type of the user data, which provides security for each individual user data type. For example, if user data is an application, then security is ensured for each of a plurality of applications recorded on the same information recording medium.
The above object can also be fulfilled by an information recording method for scrambling user data and recording the scrambled user data onto an information recording medium, the information recording medium including a first sector which stores a medium identifier unique to the information recording medium and a plurality of second sectors each of which has a unique sector number and is used for storing user data, the information recording method including: an initial value determining step for determining an initial value based on the medium identifier and a sector number of a second sector into which the user data is to be recorded; a random number generating step for generating a sequence of random numbers from the initial value; a scrambling step for scrambling the user data using the sequence of random numbers; and a recording step for recording the scrambled user data into the second sector.
With this construction, user data is scrambled with a data scramble key that differs not only for each information recording medium but also for each sector. This makes it difficult for unauthorized users to reproduce data.
The above object can also be fulfilled by an information reproducing apparatus for reproducing user data recorded on an information recording medium, the information recording medium including a first sector which stores a medium identifier unique to the information recording medium and a plurality of second sectors each of which has a unique sector number and is used for storing user data in a scrambled form, the information reproducing apparatus including: an initial value determining unit for determining an initial value based on the medium identifier and a sector number of a second sector in which the user data to be reproduced is stored in a scrambled form; a random number generating unit for generating a sequence of random numbers from the initial value; and a reproducing unit for reading the scrambled user data from the second sector, descrambling the scrambled user data using the sequence of random numbers, and reproducing the descrambled user data.
With this construction, user data that has been scrambled with a data scramble key which differs not only for each information recording medium but also for each sector can be reproduced properly.
The above object can also be fulfilled by an information reproducing method for reproducing user data recorded on an information recording medium, the information recording medium including a first sector which stores a medium identifier unique to the information recording medium and a plurality of second sectors each of which has a unique sector number and is used for storing user data in a scrambled form, the information reproducing method including: an initial value determining step for determining an initial value based on the medium identifier and a sector number of a second sector in which the user data to be reproduced is stored in a scrambled form; a random number generating step for generating a sequence of random numbers from the initial value; and a reproducing step for reading the scrambled user data from the second sector, descrambling the scrambled user data using the sequence of random numbers, and reproducing the descrambled user data.
With this construction, user data that has been scrambled with a data scramble key which differs not only for each information recording medium but also for each sector can be reproduced properly.
The above objects can also be fulfilled by a medium identifier recording apparatus for recording a unique medium identifier onto an information recording medium that includes a first sector for storing the medium identifier, including: an initial value determining unit for determining an initial value based on predetermined data and a sector number uniquely given to the first sector; a random number generating unit for generating a sequence of random numbers from the initial value; a scrambling unit for scrambling the medium identifier using the sequence of random numbers; and a recording unit for recording the scrambled medium identifier into the first sector.
With this construction, the medium identifier used for the generation of the data scramble key is scrambled and stored in the information recording medium, with it being possible to provide a high level of security for data recorded on the information recording medium.